honeywell rodgers presentation.pdf

7/27/2019 Honeywell Rodgers Presentation.pdf

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reven on

MeasuresOverview of Explosion Prevention MeasuresSlide 1Oct 2010

Sam RodgersHoneywell


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ExplosionExplosion

Explosion The bursting or rupture of anenc osure or a con a ner ue o e eve opmenof internal pressure from a deflagration

ISO

Oxidant

ATIO

DetectionFuel

Ignition

N

ContainmentContainment

Overview of Explosion Prevention MeasuresSlide 2Oct 2010



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Explosion Protection Systems DocumentsExplosion Protection Systems Documents

NFPA 68 Standard on Ex losion

Protection by Deflagration Venting (2007edition)

NFPA 69 Standard on Ex losionPrevention Systems (2008 edition)

Invoked by other Standards



, , , , ,


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Explosion Protection and PreventionExplosion Protection and Prevention

There are two distinct phases involved in a

Prevention, which deals with the elimination of theconditions which permit the formation of anexp os ve m xture an t e e m nat on o a poss esources of ignition

Protection, which deals with reducin the effects ofan explosion, the basic purpose of this guide

This talk deals with both aspects NFPA 68

methods for both protection and prevention




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PerformancePerformance--based approachbased approach

Standards offer option for compliance -

Establish life safety and property protectionobjectives

Define deflagration hazard scenario

See Chapter 5 of NFPA 68 or 69

-Use the equations as presented in Chapters 7, 8,

and 9 to determine vent requirements accordingto NFPA 68

Use the explosion prevention and protectionmethods of Chapters 7 through 14 of NFPA 69




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Explosion PreventionExplosion Prevention

Pre-Deflagration Detection and Ignit ion Control Detect using Optical or Concentration sensors Used for Pre-emptive Shutdown or Modification of

operations to Prevent Activating a Protection System

Can be used independently to reduce frequency of

Deflagrations System

Can not interfere with the operation of the ValidatedSystem

Can not be used as the sole detector for a ValidatedSystem




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Oxidant Concentration Control (Inerting)Oxidant Concentration Control (Inerting)




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Limiting Oxygen Concentration of Selected Dust SamplesLimiting Oxygen Concentration of Selected Dust Samples

us o .

Pear wood 16.0

Barium dust 13.4

Wood grinding dust 13.0

Zinc stearate 11.5Polyethylene 10.0

Para-formaldehyde 6.0

.




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Oxidant Concentration ControlOxidant Concentration Control

on nuous 2 oncen ra on on or For LOC > 5%:

Max% O2 = Worst Credible Case LOC 2 vol%

For LOC < 5%:

Max% O2 = 0.60 LOC

Without Continuous O2 Concentration Monitor

For LOC > 5%:ax 2 = .

For LOC < 5%:

Max% O2 = 0.40 LOC

And O2 Checked on a regularly scheduled basis

Requires Purge Gas Monitoring and



Alarm for Abnormal Operation


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Combustible Concentration ControlCombustible Concentration Control

With Continuous Concentration Monitor ax om us e oncen ra on =

Requires anAlarm, but not automatic action

With Continuous Concentration Monitorand SafetyInterlocks (automatic change to safe condition)

Max Combustible Concentration = 60% LFL MEC Aluminum per NFPA-484 = 50% LFL (MEC)

Requires Instrumentation to Monitor




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Predeflagration Detection and ControlPredeflagration Detection and Control

Optical system detectors are sensitive toradiant energy from hot particles, glows,

,

Extinguishing mediums such as water, carbon,

Stop and diverter valves are also common

Gas sensin s stems detect the formation ofthermal decomposition gases

Control can be accomplished with alarms,

automated shutdown, or the release of theextinguishing system




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Gas Sensing Equipment ConsiderationsGas Sensing Equipment Considerations

The system shall take air samples at inlets and

concentration for selected thermaldecomposition products.

The design shall be based on such factors as:Process mass flowFlow velocityPotential measurement interferences

Air flow and exchange rateSensor response time




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Deflagration Containment Based on PDeflagration Containment Based on Pmaxmax

PR max

test

max .

Ptest = initial absolute pressure during the test (typically 1 bar)

(1) For most gas/air mixtures, the value of R shall be 9.

(2) For St-1 and St-2 dust/air mixtures, the value of R shall

.

(3) For St-3 dust/air mixtures, the value of R shall be 13.

A value for R other than the values specified shall be

ermitted to be used if such value can be substantiated b



test data or calculations.


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Design Strength of Vessels to Contain PDesign Strength of Vessels to Contain Pmaxmax

(1) If permanent deformation, but not rupture, of the enclosurecan be accepted.

ua

mawpF

PPR

P3

20

Pmawp = enclosure design pressure [barg (psig)] according toASME Boiler and Pressure Vessel Code, i.e. the maximum

allowable workin ressure

Fu = ratio of ultimate stress of the enclosure to the allowablestress of the enclosure per the ASME Boiler and PressureVessel Code; For vessels fabricated of low-carbon steel and

low-alloy stainless steel, Fu equals approximately 3.5

P0 = worst case initial vessel pressure



Pa = atmospheric pressure


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Design Strength of Vessels to Contain PDesign Strength of Vessels to Contain Pmaxmax

(2) Ifpermanent deformation of the enclosure cannot beaccepted.

PPR

y

amawp

F

P

32

Fy = ratio of the yield stress of the enclosure to the allowable

stress of the materials of construction of the enclosure per the

ASME Boiler and Pressure Vessel Code; For vesselsfabricated of low-carbon steel and low-alloy stainless steel, Fyequals approximately 1.75

nc osures vesse s a e nspec e aleast every 3 years More frequent than



co e


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2007 Equations Summary2007 Equations Summary

Basic

75.0

154.11101 max4/33/44

0

red

StstatvP

VKPA

Enclosure L/D 2

095.0exp26.0 red

v

v

PDA

Vent Panel Mass2.03.0

5.06.0

0

0075.01red

St

v

v

PVn

KM

A

A

Partial Volume

(locally dusty)

1

31 rr

v XXA

A

Vent Ducts4.08.018.11 KEE

Av



00v


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Basic EquationBasic Equation

154.11101max4/3

3/440

red

StstatvP

PVKPA

where: Av0 = vent area calculated from the basic equation (m2) Pstat = nominal static burst pressure of the vent (bar) KSt = deflagration index (bar-m/sec) = 3

Pmax = maximum pressure of a deflagration (bar) Pred = reduced pressure after deflagration venting (bar)




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PPredred and Vent Areaand Vent Area




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Enclosure L/D CorrectionEnclosure L/D Correction

)95.0exp(26.012

.

01 redvv PD

LAA

V = 12.35 m3

=

V = 12.35 m3

=

No correction if L/D < 2

..



determines the effective L/D


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Vent Panel InertiaVent Panel Inertia

Correction Threshold is 5% effect on Vent Area

67.1

Panel Inertia Correction

5.0

..67.6

St

redT

K

nP

]0075.01[

5.06.0

23 Stvv

KMAA

Limitations: < 2

..

redn

75 < KSt < 800 bar-m/sec




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Partial VolumePartial Volume

Dust concentrations in some process equipment andbuildings are inherently or by housekeeping limitedto only a fraction, Xr, of the enclosure volume.

1

31

34r

rvv XAA

Av4 = vent area for partial volume deflagration

Av3 = vent area for full volume deflagration

=

Ventin is not re uired if Xr